The HN submission links directly to https://google.github.io/eng-practices/review/reviewer/ but if you start at the top namely https://google.github.io/eng-practices/ then there's a Terminology section right there on the first page. Maybe the GitHub Pages theme used by this site should be changed to one in which where every page links to its parent page (right now there doesn't seem to be any way to navigate upwards except by editing the URL).